Magnetic head structure with enlarged insulating layer

ABSTRACT

A magnetic head structure has a coil and a magnetic pole allowing a magnetic flux generated by the coil to be transmitted therethrough and forming a magnetic gap. An insulating layer surrounds the coil, and a protective layer covers the insulating layer and the magnetic pole. The insulating layer has a volume equal to or greater than a value which is determined with respect to a thickness of the protective layer. It is preferable to increase the volume of the insulating layer as the thickness of the protective layer is made greater. By increasing the volume of the insulating layer, the protrusion of a portion of a floating surface of the magnetic head slider near the magnetic pole, toward the disk, is reduced.

This is a divisional of application Ser. No. 10/925,564, filed Aug. 25,2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic head structure.

2. Description of the Related Art

A magnetic disk apparatus includes a plurality of disks and a pluralityof magnetic head structures arranged between the disks. The magnetichead structure is arranged in a magnetic head slider. The surface of themagnetic head slider facing the disk is called a floating surface. Themagnetic head structure comprises a coil, a magnetic pole allowing amagnetic flux generated by the coil to be transmitted therethrough andforming a magnetic gap, an insulating layer surrounding the coil, and aprotective layer covering the insulating layer and the magnetic pole,with these members being provided on a substrate forming the magnetichead slider. Also, a shield and a reading element (MR element) arearranged on the substrate.

When data are written into the disk, an electric current is supplied tothe coil. The electric current flowing through the coil generates amagnetic flux, and the magnetic flux leaking in the magnetic pole writesdata in the disk. Also, when data are read from the disk, data is readby the MR element. Recently, the flying height (amount of the floating)of the magnetic head slider has been reduced in order to increase therecording density, and the flying height is ten and several nm, forexample.

In the magnetic head structure, the substrate is made of Al₂O₃—TiC, thecoil is made of copper, the magnetic pole and the shield are made of amagnetic material such as NiFe, the protective layer is made of alumina,and the insulating layer is made of a resin material such as aphotoresist. In this manner, the whole magnetic head structure iscovered by a protective layer made of alumina, and the coil and theinsulating layer, which have coefficients of thermal expansion differentfrom that of the protective layer, are arranged within the magnetic headstructure.

The coefficient of thermal expansion of alumina is 5.8×10⁻⁶, thecoefficient of thermal expansion of copper is 17.2×10⁻⁶, the coefficientof thermal expansion of Permalloy as a magnetic material is 10×10⁻⁶, andthe coefficient of thermal expansion of a photoresist is 30-70×10⁻⁶. Thecoefficient of thermal expansion of copper or a magnetic material isapproximately two or three times greater than that of alumina. Thecoefficient of thermal expansion of photoresist is approximately 10times greater than that of alumina.

When the temperature of the interior in the magnetic disk apparatusrises or when the temperature rises due to the supply of the electriccurrent, thermal deformation may occur in the magnetic head structuredue to the difference in coefficients of thermal expansion of theconstituent materials of the magnetic head structure. Such thermaldeformation may cause deformation of the floating surface.

In considering the deformation in the floating surface, the insulatinglayer comprising a photoresist and having the greatest coefficient ofthermal expansion expands to the greatest degree, and therefore, such aphenomena occurs that a portion of the floating surface where themagnetic pole protrudes toward the disk. If the deformation in thefloating surface occurs, the minimum amount of the floating of themagnetic head slider is substantially reduced, and it is possible that aportion of the floating surface near the magnetic pole contacts thedisk, and the reliability may be reduced.

Therefore, it is desirable to reduce the protrusion of the portion ofthe floating surface near the magnetic pole toward the disk.

Conventionally, there is a proposal to reduce the protrusion of theportion of the floating surface near the magnetic pole toward the disk,by changing the materials of the insulating layer and the protectivelayer. For example, the protective layer is divided into two portions,in which a material having higher Young's modulus is used for theportion near the floating surface and a material having lower Young'smodulus is used for the portion remote from the floating surface (referto Japanese Unexamined Patent Publication (Kokai) No. 2000-306213, forexample). Also, these is a proposal to use a resin having a lower glasstransition temperature for the insulating layer (refer to JapaneseUnexamined Patent Publication (Kokai) No. 2000-306215, for example).However, as there is a large difference between coefficient of thermalexpansion of the protective layer and that of the insulating layer, asdescribed above, the problems of the thermal deformation cannot befundamentally solved even if a difference between coefficient of thermalexpansion of the protective layer and that of the insulating layer isslightly reduced.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a magnetic headstructure by which the protrusion of a portion of a floating surfacenear a magnetic pole toward a disk can be reduced.

A magnetic head structure, according to the present invention, comprisesa coil, a magnetic pole allowing a magnetic flux generated by the coilto be transmitted therethrough and forming a magnetic gap, an insulatinglayer surrounding the coil, and a protective layer covering theinsulating layer and the magnetic pole, wherein the insulating layer hasa volume equal to or greater than a value which is determined withrespect to a thickness of the protective layer.

In this arrangement, it is possible to reduce the protrusion of aportion of a floating surface near a magnetic pole, toward a disk, byincreasing the volume of the insulating layer to more than a certainvalue. It will be usually conceived that the amount of the thermalexpansion may increase when the volume of the insulating layer isincreased, so that the amount of the protrusion of a portion of afloating surface near a magnetic pole toward a disk will be increased.The inventors of the present application have found that the expansionof the insulating layer in the high temperature state occurs not only inthe direction toward the floating surface but also in the directiontransverse to the floating surface. If the volume of the insulatinglayer is increased, a component of the insulating layer, which expandsin the direction transverse to the floating surface, locally pressesupward the protective layer located above the insulating layer, so thata moment, which causes a portion of the protective layer on the side ofthe floating surface to rotate, occurs. By this moment, the outer edgeof the floating surface deforms toward the disk and the protrusion of aportion of a floating surface near a magnetic pole toward a disk isrestricted. Therefore, by increasing the volume of the insulating layerhaving a greater coefficient of thermal expansion, it is possible toreduce the protrusion of a portion of a floating surface near a magneticpole toward a disk. Also, it is necessary to increase the volume of thematerial of the insulating layer as the thickness of the protectivelayer covering the insulating layer is greater, in order to deform theprotective layer to reduce the protrusion of a portion of a floatingsurface near a magnetic pole toward a disk.

A magnetic head structure, according to the present invention, comprisesa coil, a magnetic pole allowing a magnetic flux generated by the coilto be transmitted therethrough and forming a magnetic gap, an insulatinglayer surrounding the coil, and a protective layer covering theinsulating layer and the magnetic pole, wherein the coil has an innercoil part and an outer coil part and the width of the outer coil part isgreater than two times the width of the inner coil part.

In this arrangement, the coil has a wider portion (the outer coil part),and the resistance of the coil is reduced. As the resistance of the coilis reduced, the amount of the heat generated by the coil is reduced, andas a result, the amount of the expansion of the insulating layer isreduced and the thermal deformation of the magnetic head structure isalso reduced. Therefore, it is possible to reduce the protrusion of theportion of the floating surface, near the magnetic pole, toward thedisk.

A magnetic head structure, according to the present invention, comprisesa coil, a magnetic pole allowing a magnetic flux generated by the coilto be transmitted therethrough and forming a magnetic gap, an insulatinglayer surrounding the coil, a protective layer covering the insulatinglayer and the magnetic pole, and a material layer arranged in or on theprotective layer and having coefficient of thermal expansion smallerthan that of the protective layer.

In this arrangement, the material layer having coefficient of thermalexpansion smaller than that of the protective layer suppresses thethermal expansion of the whole magnetic head structure, and therefore,it is possible to reduce the protrusion of a portion of a floatingsurface, near a magnetic pole, toward a disk.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be explained with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic view illustrating a part of a magnetic diskapparatus according to an embodiment of the present invention;

FIG. 2 is a perspective view illustrating the magnetic head slider;

FIG. 3 is a cross-sectional view illustrating the magnetic headstructure;

FIG. 4 is a cross-sectional view illustrating a modified example of themagnetic head structure;

FIG. 5 is a cross-sectional view illustrating a modified example of themagnetic head structure;

FIG. 6 is a cross-sectional view illustrating a modified example of themagnetic head structure;

FIG. 7 is a cross-sectional view illustrating a modified example of themagnetic head structure;

FIG. 8 is a cross-sectional view illustrating a modified example of themagnetic head structure;

FIG. 9 is a view illustrating a thermal deformation of a magnetic headstructure according to the prior art and illustrating the principle ofthe present invention;

FIG. 10 is a view illustrating the relationship between the volume ofthe insulating layer and the displacement of the portion of the floatingsurface near the magnetic pole when the thickness of the protectivelayer is changed;

FIG. 11 is a view illustrating the displacement of the portion of thefloating surface of the present invention and that of the prior art;

FIG. 12 is a view illustrating the upper coil of the two-layered coil;

FIG. 13 is a view illustrating the lower coil of the two-layered coil;

FIG. 14 is a view illustrating the displacement of the portion of thefloating surface of the present invention and that of the prior art;

FIG. 15 is a cross-sectional view illustrating the magnetic headstructure according to another embodiment of the present invention;

FIG. 16 is a cross-sectional view illustrating a modified example of themagnetic head structure;

FIG. 17 is a cross-sectional view illustrating a modified example of themagnetic head structure; and

FIG. 18 is a view illustrating the displacement of the portion of thefloating surface of the present invention and that of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of the present invention will now be explainedwith reference to the accompanying drawings. FIG. 1 is a schematic viewillustrating a part of a magnetic disk apparatus according to anembodiment of the present invention. FIG. 2 is a perspective viewillustrating the magnetic head slider.

The magnetic disk apparatus 10 includes magnetic disks 12 and magnetichead sliders 14. The magnetic head slider 14 has a floating surface 16and a floating rail (not shown). In operation, the disk rotates in thedirection shown by the arrow X, and the magnetic head slider 14 floatswith respect to the disk 14 with the floating amount Y and the pitchangle Z. The floating amount Y is approximately 10 nm, for example.

The magnetic head slider 14 comprises a substrate 18 forming a sliderbody and a magnetic head structure 20 provided on the substrate 18. Themagnetic head structure 20 is formed by laminating thin films of severalmaterials. The magnetic head structure 20 has a coil 22 formed on theend of the substrate 18, and a magnetic pole 26 allowing a magnetic fluxgenerated by the coil 22 to be transmitted therethrough and forming amagnetic gap 24. Also, a shield 28 and a reading element (MR element) 30are arranged on the substrate 18.

When data are written into the disk 12, an electric current is suppliedto the coil 22. The electric current flowing through the coil 22generates a magnetic flux, and the magnetic flux leaking in the magneticgap 24 of the magnetic pole 26 writes data in the disk 12. Also, whendata are read from the disk 12, data is read by the reading element 30.Recently, the amount of the floating of the magnetic head slider 14 hasbeen reduced in order to increase the recording density, and the amountof the floating is ten and several nm, for example.

FIG. 3 is a cross-sectional view illustrating the magnetic headstructure 20. The substrate 18 corresponds to only a part of thesubstrate 18 shown in FIGS. 1 and 2. The magnetic head structure 20 hasthe coil 22 and the magnetic pole 26. The coil 22 is of a two-layeredstructure comprising an upper coil 22U and a lower coil 22L, and thecentral portions of the upper coil 22U and the lower coil 22L areconnected to each other. Also, two layers of the shield 28 are providedon the substrate 18, and the reading element (MR element) 30 is arrangedbetween the two layers of the shield 28.

Also, the magnetic head structure 20 includes an insulating layer 32surrounding the coil 22, and a protective layer 34 covering theinsulating layer 32 and the magnetic pole 22. The insulating layer 32comprises a two-layered structure corresponding to the two-layered coil22 (22U and 22L). These elements are formed by laminating thin films ofrespective materials. The protective layer 34 has a considerablethickness and is also formed between the above described several layers.

The substrate 18 is made of Al₂O₃—TiC, the coil 22 is made of copper,the magnetic pole 26 and the shield 28 are made of a magnetic materialsuch as NiFe, the protective layer 34 is made of alumina, and theinsulating layer 32 is made of a resin material such as a photoresist.The whole magnetic head structure 20 is covered by the protective layer34 such as alumina, and the coil 22 and the insulating layer 32, whichhave coefficients of thermal expansion different from that of theprotective layer 34, are arranged within the magnetic head structure 20.The coefficient of thermal expansion of alumina forming the protectivelayer 34 is 5.8×10⁻⁶, the coefficient of thermal expansion of copperforming the coil 22 is 17.2×10⁻⁶, the coefficient of thermal expansionof Permalloy as a magnetic material forming the magnetic pole 26 and theshield 28 is 10×10⁻⁶, and the coefficient of thermal expansion of aphotoresist forming the insulating layer 32 is 30-70×10⁻⁶. Thecoefficient of thermal expansion of copper or a magnetic material isapproximately two or three times greater than that of alumina. Thecoefficient of thermal expansion of photoresist is approximately 10times greater than that of alumina.

The insulating layer 32 has a volume equal to or greater than a valuewhich is determined with respect to a thickness of the protective layer34, so that the protrusion of a portion of the floating surface 16 wherethe magnetic pole 26 is positioned is reduced. In FIG. 3, the insulatinglayer 32 has a uniform thickness and is formed longer than the regionwhere the coil 22 is provided in the cross-section of FIG. 3. That is,the insulating layer 32 has a volume considerably greater than a volumenecessary to insulate the coil 22.

FIG. 9 is a view illustrating a thermal deformation of a magnetic headstructure according to the prior art and illustrating the principle ofthe present invention. The constituent elements of the magnetic headstructure are represented by reference numerals identical to those ofFIG. 3. The volume of the insulating layer 32 of FIG. 9 is smaller thanthat of the insulating layer 32 of FIG. 3. FIG. 9 is a view in which thethermal deformation is calculated, using the definite element method. InFIG. 9, it will be understood that a thermal deformation occurs, due tomainly the difference between the coefficient of thermal expansion ofthe insulating layer 32 and that of the protective layer 34. Inparticular, the deformation occurs such that a portion 16A of thefloating surface 16 near the magnetic pole 26 protrudes to the greatestdegree toward the disk 12, as shown by the arrow A. The amount of thefloating of the magnetic head slider 14 is about ten and several nm, andif the amount of the protrusion of the portion 16A becomes greater, itcan be said that the minimum amount of the floating of the magnetic headslider 14 is substantially reduced, and the portion 16A of the floatingsurface 16 where the coil 22 is positioned may contact the disk 12.

In the present invention, the protective layer 34 is deformed in amanner as shown by the broken line in FIG. 9, by increasing the volumeof the insulating layer more than a certain value, and it is possible toreduce the protrusion of the portion 16A of the floating surface 16 nearthe magnetic pole 26 in the direction shown by the arrow A. Therefore,the reliability of the operation of the magnetic head structure 20 isfurther improved.

It will be usually conceived that the amount of the thermal expansion ofthe insulating layer 32 may increase when the volume of the insulatinglayer 32 is increased, so that the amount of the protrusion of theportion 16A of the floating surface 16 near the magnetic pole 26 will beincreased. The inventors of the present application have found that theexpansion of the insulating layer 32 in the high temperature stateoccurs not only in the direction toward the floating surface 16 but alsoin the direction transverse to the floating surface 16.

If the volume of the insulating layer 32 is increased, a component ofthe insulating layer 32, which expands in the direction transverse tothe floating surface 16, locally presses upward a part of the protectivelayer 36 located above the insulating layer 32, so that a moment M,which causes a portion of the protective layer 32 on the side of thefloating surface 16 to rotate, occurs. By this moment M, the outer edgeof the floating surface 16 (left upper end of the protective layer 34 inFIG. 9), deforms toward the disk 12 and the protrusion of the portion16A of the floating surface 16 near the magnetic pole 26 toward the disk12 is restricted.

Therefore, by increasing the volume of the insulating layer 32 having agreater coefficient of thermal expansion, it is possible to reduce theprotrusion of the portion 16A of the floating surface 16 near themagnetic pole 26 toward the disk 12. Also, it is necessary to increasethe volume of the material of the insulating layer 32, as the thicknessof the protective layer 34 covering the insulating layer 32 is greater,in order to deform the protective layer 34 so as to reduce theprotrusion of the portion 16A of the floating surface 16 near themagnetic pole 26 toward the disk 12.

FIG. 10 is a view illustrating the relationship between the volume ofthe insulating layer 32 (insulator volume) and the displacement of theportion 16A of the floating surface 16 near the magnetic pole 26(displacement of point A) when the thickness of the protective layer 34is changed. The displacement of the portion 16A is the amount of theprotrusion, measured in the direction of the arrow A in FIG. 9. Thethicknesses of the protective layer 32 are 6.25 μm, 12.5 μm, and 25 μm.From the result shown in FIG. 10, it will be understood that the amountof the protrusion of the portion 16A has a local minimum value at acertain value of the volume of the protective layer 34. Also, the localminimum value of the protrusion of the portion 16A shifts to the sidewhere the volume of the protective layer 34 becomes greater, as thethickness of the protective layer 34 is greater.

Therefore, the characteristic feature of the present invention is to aimfor a reduction of the amount of the protrusion of the portion 16A,using this mechanism. However, if the volume of the insulating layer(photoresist) 32 is too large, the effect of reducing the amount of theprotrusion of the portion 16A cannot be expected, and it is important toset the volume of the insulating layer 32 within the certain rangeincluding the local minimum value, in accordance with the thickness ofthe protective layer 34.

As a result of analyzing the result of FIG. 10, it has been foundpreferable that the volume of the insulating layer 32 is in the range of10 times to 40 times of a value defined by the cube of L, where L is thethickness of the protective layer 34 and is smaller than 25 μm. In thiscase, the thickness L is a thickness of a portion of the protectivelayer 34 above the magnetic pole 26, as shown in FIG. 3. Note that thisresult is optimum in the magnetic head structure 20 in which thethickness of the protective layer 34 is smaller than 25 μm.

FIG. 11 is a view illustrating the displacement of the portion of thefloating surface of the present invention and that of the prior art. Themagnetic head structure 20 of the present invention is constructed suchthat the thickness of the protective layer 34 is 12.5 μm and the volumeof the insulating layer 32 is 3.26 E-05 mm³. The conventional magnetichead structure is constructed such that the thickness of the protectivelayer 34 is 12.5 μm and the volume of the insulating layer 32 is 2.85E-06 mm³ (standard volume of the insulating layer arranged around thecoil 22). According to the present invention, the amount of theprotrusion of the portion 16A is reduced by approximately 30%.

In increasing the volume of the insulating layer 32, it is not necessaryto intensively arrange the material of the insulating layer 32 at oneportion, but it is possible to arrange the material of the insulatinglayer 32 into a plurality of divided portions. FIGS. 4 to 8 showexamples of the magnetic head structure in which the material of theinsulating layer 32 is differently arranged and the volume of theinsulating layer 32 is increased.

FIG. 4 is a cross-sectional view of the magnetic head structure. In FIG.4, the volume of the upper part of the insulating layer 32 surroundingthe upper coil 22U is increased, and the volume of the lower part of theinsulating layer 32 surrounding the lower coil 22L is maintainedunchanged with respect to the conventional one.

FIG. 5 is a cross-sectional view of the magnetic head structure. In FIG.5, the volume of the upper part of the insulating layer 32 surroundingthe upper coil 22U is maintained unchanged with respect to theconventional one, and the volume of the lower part of the insulatinglayer 32 surrounding the lower coil 22L is increased.

FIG. 6 is a cross-sectional view of the magnetic head structure. In FIG.6, the volume of the upper part of the insulating layer 32 surroundingthe upper coil 22U and the volume of the lower part of the insulatinglayer 32 surrounding the lower coil 22L are maintained unchanged withrespect to conventional ones, and an additional insulating layer 32A isprovided in a plane substantially coplanar with the plane of theinsulating layer 32.

FIG. 7 is a cross-sectional view of the magnetic head structure. In FIG.7, the volume of the upper part of the insulating layer 32 surroundingthe upper coil 22U and the volume of the lower part of the insulatinglayer 32 surrounding the lower coil 22L are maintained unchanged withrespect to the conventional ones, and an additional insulating layer 32Bis provided above the insulating layer 32. The additional insulatinglayer 32A or 32B does not directly insulate the coil 22, but is madefrom the same material as the insulating layer 32 and has the effectsimilar to that when the volume of the insulating layer 32 is increased.

FIG. 8 is a cross-sectional view of the magnetic head structure. In FIG.8, the single layer coil 22 is provided, and the volume of the singlelayer insulating layer 32 surrounding the coil 22U is increased. In thecase of the single layer coil 22 too, an effect similar to that of themulti-layered coil 22 is obtained.

FIG. 12 is a view illustrating the upper coil of the two-layered coil,and FIG. 13 is a view illustrating the lower coil of the two-layeredcoil. The inner end of the upper coil 22U and the inner end of the lowercoil 22L are connected to each other. The upper coil 22U and the lowercoil 22L of FIGS. 12 and 13 can be used as the upper coil 22U and thelower coil 22L of FIGS. 3 to 7, or they can be used as the conventionaltwo-layered coil.

Each of the upper coil 22U and the lower coil 22L has a connecting line22 a and a coil portion 22 b. The coil portion 22 b has an outer coilpart 22 i and an outer coil part 22 o. Each of the upper coil 22U andthe lower coil 22L is formed such that the width W of the outer coilpart 22 o is greater than two times of the width w of the inner coilpart 22 i.

Also, the width of a portion 22 n of the connecting line 22 a near theouter coil part 22 o is greater than the width of the outer coil part 22o. In particular, in the upper coil 22U, the width of a portion 22 n ofthe connecting line 22 a near the outer coil part 22 o is greater thanthe width of other portion 22 p of the connecting line 22 a.

In this arrangement, the coil 22 has a wider portion (the outer coilpart 220), and the resistance of the coil 22 is reduced. As theresistance of the coil 22 is reduced, the amount of the heat generatedby the coil 22 is reduced and, as a result, the amount of the expansionof the insulating layer 32 is reduced and the thermal deformation of themagnetic head structure 20 is also reduced. Therefore, it is possible toreduce the protrusion of the portion 16A of the floating surface 16 atwhich the coil 22 is positioned (see FIG. 9).

In this manner, when an electric current is supplied to the coil 22, thecoil 22 generates heat due to the resistance thereof, the temperaturerises and, as a result, the portion 16A protrudes. The amount of theprotrusion of the portion 16A when an electric current is supplied tothe coil 22 is proportional to the amount of the generated heat(temperature rise). Therefore, the reduction of the resistance of thecoil 22 leads to the reduction of the amount of the generated heat,i.e., to the reduction of the amount of the protrusion. In the presentinvention, the resistance of the coil 22 is reduced, by adopting such astructure that the connecting line 22 a and the outer coil part 22 o ofthe coil 22 are widely spread.

In the embodiment of the present invention, the width of the outer coilpart 22 o is greater than two times of the width of the inner coil part22 i, and the size of the connecting line 22 a is maintainedsubstantially constant from its leading end to a position near theconnecting point to the outer coil part 22 o, and the size of theconnecting line 22 a is enlarged at a position just before theconnecting point to the outer coil part 22 o.

FIG. 14 is a view illustrating the displacement of the portion of thefloating surface of the present invention and that of the prior art.When an electric current of DC 60 mA is supplied, the maximumtemperature of embodiment of the present invention in which coil 22 isenlarged is reduced by 21%, compared with that of the prior art in whichcoil 22 is not enlarged. An experiment was carried out, and the resultsobtained are described in Table 1 below. TABLE 1 No Coil EnlargementCoil Enlargement Resistance (Ω) 3.0 2.4 Amount of Generated 10.8 8.6Heat (mW) Maximum Rising 13.0 10.3 Temperature (° C.)

FIG. 15 is a cross-sectional view illustrating the magnetic headstructure according to another embodiment of the present invention. Asin the magnetic head structure 20 of the former embodiment, the magnetichead structure 20 of this embodiment has a coil 22, a magnetic pole 26allowing a magnetic flux generated by the coil 22 to be transmittedtherethrough and forming a magnetic gap 24, an insulating layer 32surrounding the coil 22, and a protective layer 34 covering theinsulating layer 32 and the magnetic pole 26. Also, a two-layered shield28 is arranged on the substrate 18 and a reading element (MR element) 30is arranged between two layers of the shield 28. The coil 22 is formedon the substrate 18 via the shield 28 and a part of the protective layer34.

Further, the magnetic head structure 20 comprises at least one materiallayer 36 arranged in or on the protective layer 34 and havingcoefficient of thermal expansion smaller than that of the protectivelayer 34. The material layer 36 having smaller coefficient of thermalexpansion is preferably arranged in one continuous layer, rather thanbeing discontinuously arranged in one layer. In FIG. 15, one materiallayer 36 having smaller coefficient of thermal expansion is arranged onthe surface of the substrate 18. In this case, a part of the protectivelayer 34 is formed on the material layer 36 having smaller coefficientof thermal expansion, and the shield 28 is formed on the part of theprotective layer 34. Also, another one material layer 36 having smallercoefficient of thermal expansion is arranged on the surface of theprotective layer 34. For example, the material layer 36 having smallercoefficient of thermal expansion comprises Invar. Alternatively, thematerial layer 36 having smaller coefficient of thermal expansioncomprises a material having smaller coefficient of thermal expansionsuch as aluminum nitride (AlN), or a composite structure of aninsulating material and Invar.

The thermal expansion of the material layer 36 having smallercoefficient of thermal expansion is small when the temperature risesbecause the amount of thermal expansion is small, and suppresses thethermal expansion of the insulating layer 32 in the directionperpendicular to the floating surface 16, whereby it is possible toreduce the protrusion of the portion 16A of the floating surface 16 nearthe magnetic pole. That is, by providing the material layer 36 havingsmaller coefficient of thermal expansion, the insulating layer 32 theamount of the thermal expansion of which is greater is prevented fromexpanding to the greater extent in the direction perpendicular to thefloating surface 16, and the protrusion of the portion 16A of thefloating surface 16 near the magnetic pole is reduced. The insulatinglayer 32 can expand in the direction parallel to the floating surface16.

FIG. 18 is a view illustrating the displacement of the portion of thefloating surface of the present invention and that of the prior art.According to the embodiment of the present invention, the displacement(the amount of the protrusion) of the portion 16A of the floatingsurface 16 near the magnetic pole is greatly reduced, compared with thatof the prior art.

FIG. 16 is a cross-sectional view illustrating a modified example of themagnetic head structure. The magnetic head structure of FIG. 16 issimilar to that of FIG. 15, except for the material layer 36 havingsmaller coefficient of thermal expansion. In FIG. 16, the material layer36 having smaller coefficient of thermal expansion is arranged withinthe protective layer. The operation and the effect of this example aresimilar to those of the example of FIG. 15.

FIG. 17 is a cross-sectional view illustrating a modified example of themagnetic head structure. The magnetic head structure of FIG. 16 issimilar to that of FIG. 15, except for the material layer 36 havingsmaller coefficient of thermal expansion. In FIG. 17, the material layer36 having smaller coefficient of thermal expansion is arranged betweenthe magnetic pole 26 and the upper shield 28. The operation and theeffect of this example are similar to those of the example of FIG. 15.

In this manner, the material layer 36 having smaller coefficient ofthermal expansion is arranged on the surface of the protective layer 34.Alternatively, the material layer 36 having smaller coefficient ofthermal expansion is arranged within the protective layer.Alternatively, the material layers 36 having smaller coefficient ofthermal expansion are arranged on the surface of the protective layer 34and between the substrate 18 and the protective layer 34. Alternatively,the material layer 36 having smaller coefficient of thermal expansion isarranged on the surface of the protective layer 34 and between themagnetic pole 26 and the shield 28. Alternatively, the material layer 36having smaller coefficient of thermal expansion is arranged at anyposition within the protective layer 34 as a layer parallel to theinsulating layer 32.

1. A magnetic head structure comprising: a coil; a magnetic poleallowing a magnetic flux generated by the coil to be transmittedtherethrough and forming a magnetic gap; an insulating layer surroundingthe coil; a protective layer covering the insulating layer and themagnetic pole; and a material layer arranged in or on the protectivelayer and having coefficient of thermal expansion smaller than that ofthe protective layer.
 2. The magnetic head structure according to claim1, wherein the material layer having coefficient of thermal expansionsmaller than that of the protective layer is arranged on the protectivelayer.
 3. The magnetic head structure according to claim 1, wherein thematerial layer having coefficient of thermal expansion smaller than thatof the protective layer is arranged in the protective layer.
 4. Themagnetic head structure according to claim 1, wherein the material layerhaving coefficient of thermal expansion smaller than that of theprotective layer is arranged between the magnetic pole and a shield. 5.The magnetic head structure according to claim 1, wherein the materiallayers having coefficient of thermal expansion smaller than that of theprotective layer are arranged on the protective layer, in the protectivelayer and between the magnetic pole and a shield.
 6. The magnetic headstructure according to claim 1, wherein: the material layer is situatedbetween a substrate and a shield.